Generally, a vibration driven apparatus applied to a vibration wave motor has an vibration member in which vibration waves are formed, and a moving member which is brought into pressure contact with the vibration member, and obtains driving force by making the vibration member and the moving member frictionally driven by the vibration waves.
Therefore, a contacting portion arranged between the vibration member and the moving member extracts the driving force by repeating contact and separation with and from the vibration member while being deformed so as to follow the vibration of the vibration member.
A prior art form of a vibration wave motor of this kind is illustrated in FIG. 9A. (see Japanese Patent Application Laid-Open No. S61-224882). In FIG. 9A, a vibration member 122 is formed into an annular shape, and a plurality of protrusions 122b are formed in the upper portion of the vibration member 122 over the whole circumference of the vibration member 122.
A moving member 123 is brought into pressure contact with the vibration member 122 by a pressing member (not illustrated). The moving member 123 is configured by a ring-shaped main body portion 123a which is formed by an elastic member, a flange portion 123b which is extended from the main body portion 123a, and a contacting portion 123c which is extended from an end portion of the flange portion 123b and which has a friction surface that is brought into contact with the vibration member 122.
A piezoelectric ceramic 121 is bonded with an adhesive to the bottom surface of the vibration member 122, and generates traveling waves at the time when alternating voltages having a phase difference therebetween are applied to the piezoelectric ceramic 121 from a driving circuit (not illustrated) for driving the motor. When the traveling direction of the traveling waves is the positive direction of the θ direction (see the arrow in FIG. 9A), the moving direction of the frictionally driven moving member 123 becomes the negative direction of the θ direction.
In such a case of the moving member 123 configured to have the flange portion, the direction of trajectory of vibration generated in the vibration member 122 substantially coincides with the direction of displacement of the contacting portion of the moving member 123 when viewed on the plane formed by the radial direction and the vertical direction in the cylindrical coordinate system centering on the rotation axis of the moving member. When the direction of vibration trajectory substantially coincides with the direction of displacement, the sliding in the radial direction on the friction surface can be reduced to prevent deterioration of efficiency.
Further, a configuration of a moving member of a vibration wave motor in another prior art form is illustrated in FIG. 9C (see Japanese Patent Application Laid-Open No. 2002-315364).
In FIG. 9C, a plurality of contacting portions 133c which are brought into contact with the vibration member and which have predetermined spring stiffness are concentrically provided at a moving member 133.
Since the plurality of contacting portions 133c are provided, the contact area is increased, and the surface pressure of the contacting portions is reduced. Thereby, the wear of the contacting portions 133c is reduced to improve the durability of the vibration wave motor.
However, the contacting portion of the vibration wave motor of the prior art form illustrated in FIG. 9A as described above is configured to have a cantilever section having a predetermined contact width.
The contacting portion 123c of the moving member 123 is brought into contact with the vibration member 122, as illustrated in FIG. 9B.
In this case, only the vicinity of the outer diameter side edge portion of the friction surface of the contacting portion 123c is brought into contact by strong pressure with the vibration member 122, and hence the whole friction surface is not brought into uniform contact with the vibration member 122.
Therefore, even when the contact area of the contacting portion 123c is increased by simply enlarging the contacting portion 123c so as to reduce the surface pressure applied to the friction surface, for the purpose of improving the durability of the vibration wave motor, the contact area is not increased and the surface pressure is not reduced because the friction surface is brought into contact with the vibration member 122 only in the vicinity of the outer diameter side edge portion of the friction surface.
Further, when the width of the contacting portion 123c is increased, even in the case where the wear in the vicinity of the outer diameter side edge portion of the contacting portion 123c progresses and the whole friction surface of the contacting portion 123c is brought into contact with the vibration member 122, the portion of the friction surface, in which portion the direction of vibration trajectory of the vibration member 122 does not coincide with the direction of displacement of the contacting portion 123c, is increased.
This causes reduction of efficiency and generation of squealing sounds, and also causes wear. Thus, it is necessary to reduce, as a whole, the pressure force applied to the vibration member so that the friction is stabilized even at the outer diameter side edge portion of the contacting portion 123c at which the edge portion is brought into contact with the vibration member by strong pressure.
The output torque may be considered to be substantially proportional to the applied pressure force. Thus, when the applied pressure force is reduced, the output torque of the vibration wave motor is also restricted.
On the other hand, in the contacting portion 133c of the vibration wave motor of the prior art form illustrated in FIG. 9C as described above, the plurality of contacting portions are provided, and hence the contact area can be increased to improve the durability of the vibration wave motor.
Further, the direction of displacement of the respective contacting portions can be made coincident with the direction of vibration trajectory of the vibration member, so that the sliding in the radial direction on the friction surface can be reduced.
However, each of the contacting portions 133c has a cantilever section similarly to the vibration wave motor of the prior art form illustrated in FIG. 9A as described above. Thus, the local wear may be caused in dependence upon the contact state between the vibration member and the contacting portion 133c as illustrated in FIG. 9B, so as to deteriorate the performance of the vibration wave motor.
As described above, in the configuration of the contacting portion of the conventional vibration wave motor, there is a problem that the durability of the vibration wave motor is deteriorated by the local wear of the contacting portion.